The Open Systems Interconnection model (OSI model) includes seven different layers. The layers, in general, serve as a way to segment communication systems into different parts. Listed in order from one to seven, these layers include the physical layer, the data link layer, the network layer, the transport layer, the session layer, the presentation layer, and the application layer. Each layer can provide particular services to the layer above, e.g., where layer “N” can provide services to layer “N+1.” Further, each layer can request services from the layer below, e.g., where layer “N” can request services from layer “N−1.”
The physical layer is the first layer of the OSI model and is also referred to as the “PHY.” The PHY defines the electrical and physical specifications for devices. The PHY generally defines the relationship between a device and a transmission medium, such as a copper or optical cable. For example, the PHY can include, or define, pin layouts, voltages, cable specifications, hubs, network adapters, or the like.
In one example, the PHY can include a sub-layer referred to as the Physical Coding Sublayer (PCS). In general, the PCS can perform functions or services such as auto-negotiation and coding. In some cases, the width of the data path of the PHY is not the same as the width of the PCS. Consider an example in which a transceiver PHY is configured to convert serial data at 28 gigabits per second (Gbps) to 40-bit parallel words with a 700 MHz clock. The PCS circuitry, however, may be configured to work with 66-bit words. Thus, a data transformation is needed to convert the 40-bit parallel words clocked with a 700 MHz clock to 66-bit words.
An adapter can be used to perform the needed data transformation. Adapter circuitry, referred to as a “gearbox,” can be included between the transceiver of the PHY and the PCS. A gearbox can be configured to adapt the width of the PHY data path to the width of the PCS data path. There are a variety of different protocols that can be implemented within the PCS circuitry. Each protocol has specific requirements as to the format, e.g., width and clock speed, used for the data path. Due to the availability of these different protocols, the type of data transformation that is needed can vary significantly based upon the requirements of the particular protocol that is implemented within the transceiver and PCS circuitry.